Enhanced high-temperature polymer electrolyte membrane for fuel cells based on polybenzimidazole and ionic liquids

Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid, 1-hexyl-3-methylimidazolium tri?uoromethanesulfonate (HMI-Tf). PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 × 10⁻² S/cm) at 250 °C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 °C, which is attractive for high-temperature (>200 °C) polymer electrolyte membrane fuel cells.